This disclosure is directed toward the measurement of concentrations of compounds in a gas sample. More particularly, the disclosure is directed toward methods and apparatus for measuring concentrations of compounds containing chlorine within a mixture of noble gases and, in particular, within a helium carrier gas which has been doped with relatively small concentrations of krypton. The disclosed system has also been used for measuring concentrations of other halogens such as fluorine. Other noble gas dopants such as xenon and argon have also been employed. Spark discharges are used to initiate a series of reactions within the carrier gas and sample mixture which results in the formation of an excited chlorine-krypton molecule which, in turn, emits characteristic photon radiation. The concentration of chlorine within the sample is then determined from the measured intensity of the characteristic photon radiation from the decay of excited chlorine-krypton. It is emphasized that the intensity of the characteristic photon radiation is proportional to the mass of chlorine within the sample. The chlorine content is, therefore, determined independently of the structure of the compound in which it is contained.
For many years, there has been a strong desire to develop gas chromatographic detectors that detect only a specific element. It is well known in the art that a gas chromatographic (GC) column is able to separate very similar compounds into separate peaks output as a function of time. This time-based separation is especially useful in delineation of adjacent peaks. Once the peaks are separated, it is necessary to identify the constituents of the peaks, and then to quantify these constituents so that concentrations of compounds or elements within the sample gas input into the GC can be determined.
Detectors which respond to chlorine are especially needed in the field of pollution monitoring and control. Chlorine pollutants in air or in water are generally in the form of organic compounds. Pollutants, however, also include a far greater variety of compounds which have chlorine in them. Common, and potentially dangerous, water and air pollutants include gaseous freons, pesticide residue in the soil, polychlorobiphenyl (often called PCB) and many others. While all of these can be extremely valuable compounds in one aspect, they can also be detrimental in trace quantities where they are not wanted. They are especially difficult to isolate, quantify and remove in trace quantities. Even trace quantities of these materials can pose significant environmental hazards in air, water, and soil.
Detectors which respond to trace amounts of chlorine are also needed in many chemical processes which utilize catalysts. Even trace amounts of chlorine can deteriorate or even destroy catalysts. As an example, in the crude oil refining industry, concentrations of chlorine as low as ten parts per million can essentially destroy or "poison" the catalyst used in refineries which produce gasoline.